4.7.1. The “keep left” (or “keep right”) sign to diagram 610 (S3‑2‑3, see Figure 4-25) may be erected without an order. It is used at traffic islands, refuges and on the central reservations of dual carriageway roads. The sign should be used at the recommencement of a central reservation following a gap, as any traffic which turns right does so in front of the sign without actually passing it. At the start of a dual carriageway, it may be accompanied by a plate with the legend “Dual carriageway”. This plate is particularly important on roads subject to the national speed limit to indicate that different speed limits may now apply. The sign is also used extensively at road works to indicate the required movement of vehicles past the works area (see Chapter 8).